The subject matter disclosed herein relates to use of a three-dimensional (3D) laser scanner time-of-flight (TOF) coordinate measurement device. A 3D laser scanner of this type steers a beam of light to a non-cooperative target such as a diffusely scattering surface of an object. A distance meter in the device measures a distance to the object, and angular encoders measure the angles of rotation of two axles in the device. The measured distance and two angles enable a processor in the device to determine the 3D coordinates of the target.
Discussed herein is a TOF laser scanner which is any type of scanner where the distance to a target point is based on the speed of light in air between the scanner and the target point. Laser scanners are typically used for scanning closed or open spaces such as interior areas of buildings, industrial installations and tunnels. They are used for many purposes, including industrial applications and accident reconstruction applications. A laser scanner can be used to optically scan and measure objects in a volume around the scanner through the acquisition of data points representing objects within the volume. Such data points are obtained by transmitting a beam of light onto the objects and collecting the reflected or scattered light to determine the distance, two-angles (i.e., an azimuth and a zenith angle), and optionally a gray-scale value. This raw scan data is collected, stored and sent to a processor or processors to generate a 3D image representing the scanned area or object. To generate the image, at least three values are collected for each data point. These three values may include the distance and two angles, or may be transformed values, such as the x, y, z coordinates. In an embodiment, a fourth value collected by the 3D laser scanner is a gray-scale value for each point measured. Such a gray-scale value is related to the irradiance of scattered light returning to the scanner.
Angular encoders are used to measure the two angles of rotation about the two axes of rotation. One type of angular encoder includes a disk and one or more read heads. In an embodiment, the disk is affixed to a rotating shaft, and the one or more read heads are affixed to a portion that is stationary with respect to the rotating shaft.
Many contemporary laser scanners also include a camera mounted on the laser scanner for gathering camera digital images of the environment and for presenting the camera digital images to an operator of the laser scanner. By viewing the camera images, the operator of the scanner can determine the field of view of the measured volume and adjust settings on the laser scanner to measure over a larger or smaller region of space if the field of view needs adjusting. In addition, the camera digital images may be transmitted to a processor to add color to the scanner image. In order to generate a color scanner image, at least six values (three positional coordinates such as x, y, z; and red value, green value, blue value or “RGB”) are collected for each data point.
The data collected by a laser scanner is often referred to as point cloud data because the data, which is typically relatively dense, may resemble a cloud. The term point cloud is taken herein to mean a collection of 3D values associated with scanned objects. The elements of the point cloud may also include additional attributes such as gray scale and color. The point cloud data may be used to produce 3D representations of the scene being scanned. Such representations may be viewed in a variety of ways, as discussed further hereinbelow. One way to represent point cloud data is to show it as a video such as a “fly-through” video in which an observer is shown a changing a two-dimensional (2D) display that produces the impression of the observer moving through space in three dimensions. Up until now such videos have been outside the control of the operator or separated from a preferred path.
Accordingly, while existing 3D scanners are suitable for their intended purposes, what is needed is a 3D scanner having certain features of embodiments of the present invention.